State-of-the-art air-augmented rocket engines obtain jet thrust by burning an organic, fuel-rich composition containing oxidizer sufficient to maintain combustion but insufficient for complete oxidation of the fuel components; ejecting the resulting fuel-rich combustion products into an afterburner; and then mixing high pressure, heated ram air with the fuel-rich products of combustion, thereby obtaining secondary combustion in the afterburner. Temperature efficiency, which is the ratio of actual combustion temperature obtained to the theoretically obtainable temperature, is directly proportional to theoretical engine performance and is therefore frequently employed to define performance efficiency. In general, such efficiency has been relatively low, ranging from about 40% to 70%, the latter being obtained under the most favorable conditions. Because of the relatively low combustion temperatures which can drop below ignition temperature of the organic fuel-rich composition, it has been the practice to employ flame stabilizers and flame holders to improve combustion efficiency and increase temperature by providing areas of turbulent mixing. Unfortunately, such expedients also result in a pressure drop which tends to decrease overall system propulsive efficiency.
The present invention increases temperature efficiency to as high as about 90% to 100%, thereby greatly improving air-augmented rocket engine performance. The improvement, furthermore, is accomplished at relatively low cost in terms of fuel-rich composition modification and can accomplish substantial savings in cost and dead weight by very considerably reducing the mixing and combustion chamber volume downstream of the fuel-rich grain presently required in the state-of-the-art air-augmented rocket engine. It is also believed that the high-temperature gaseous subfluorides improve mixing of the ram air, act as ignition aids for the ram air-organic fuel-rich combustion products, and may provide adequate turbulent mixing to make possible elimination of flame holders.
Combustible compositions of particular utility in air-augmented rocket engines comprising (a) an organic fuel-rich matrix containing insufficient oxidizer for complete combustion; and (b) solid fuel-rich particles, dispersed in the matrix, comprising at least one oxidizable solid element having a single stable valence and the ability to produce a gaseous subfluoride; and at least one solid oxidizer compound having combined therein as an oxidizer element, fluorine available to oxidize the oxidizable solid element to subfluoride; the oxidizable element and oxidizer compound being present in the fuel-rich particles in amounts sufficient to react to produce an appreciable amount of the gaseous subfluoride.